This invention concerns an improved arrangement differentially bolting together at least two machine parts by means of at least one threaded bolt which possesses at its two ends threads that differ from each other in pitch.
Machine parts are normally bolted together by means of hexagonal or cylindric head screws with or without nuts, or by means of threaded bolts with nuts. If split housings and other containers are bolted together, the bolts are usually accommodated in juxtaposed flanges which protrude beyond the container wall. If the machine parts to be bolted together require a powerful compression, a bolting by differential threads is used, for example, in the case of the so-called Hirth tooth system for crankshafts (see Dubbel: "Tashchenbuch fuer den Maschinenbau," Volume I, page 801, Fig. 198, 13th Edition, 1970), where each of the two parts to be connected under tension possesses a bore with an internal thread but where one of the two parts has a smaller screw pitch than the other. The associated threaded bolt does not have a head but possesses likewise two thread sections of different pitch. This bolt is first screwed into the part having a small screw pitch, then the second part is then placed onto the bolt end with the greater screw pitch and the threaded bolt is then screwed into it. The bolt will enter the part with the greater screw pitch at a faster rate than its rate of emerging from the part having the smaller screw pitch, with the result that the two parts will approach each other by the difference in pitch per one turn of the bolt. When the two parts are finally tightened, the transmission ratio is very high due to the effective small pitch.
These known types of threaded connections have the following disadvantages:
The use of screw bolts equipped with heads make it necessary to provide the machine parts which are to be bolted with flanges that protrude beyond the contours of these parts. If the parts are subjected to high operating temperatures and strong pressures and have large diameters, such flanges will assume dimensions that lead to localized concentrations of material, and become a potential source of wide differences in temperature when the machine is started, thereby causing inadmissible stresses and deformations.
The known arrangement of differential thread connection is applicable only for a construction where one single differentially threaded bolt is used because each turn of the bolt causes the two machine parts to move closer to each other, and if two or more bolts were to be used it would become necessary to tighten all these bolts simultaneously.